Magneto



w. OCHHSENBEIN March 3, 1942,

,MAGNETO Filed Oct. 5, 1940 gnbenn WaHev O h INVENTOR "89- ATTORNEY.

Patented Mar. 3, 1942 -MAGNETO Walter Ochsenbein, Bern to Hasler A.-G. Werke e, Switzerland, assignor fiir Telephonie & Priizisionsmechanik, Berne, Switzerland Application October 5, 1940, Serial No. 359,867 In'Switzerland October 7, 1939 2 Claims.

The present invention relates to improvements in magnetos for internal combustion engines and particularly to magnetos with multi-pole magnet and winding part the number of cylinders of the engine being smaller than the number of the flux changes produced in the magneto per every revolution of the camshaft.

Magnetos for internal combustion engines hav-- ing a relatively large number of cylinders areas a rule designed in such a manner that the number of flux changes produced in the coil cores for each revolution of the camshaft of the engine is equal to the number of ignition sparks that the magneto has to produce per ignition circuit. The primary circuit is accordingly broken on each change of flux.

It is already known to use such magnetos for engines the number of cylinders of which is an integral divisor of the number of the flux changes produced in the magneto. In this case the primary current is interrupted, for example, only on every second or third or the like flux change.

(On those flux changes which are not utilised for ignition there is a relatively strong short-circuit current in the primary winding, which greatly weakens the magnetic field.) This is not a disadvantage if the fiux changes follow one another at such great intervals that they do not affect one another. It has now been found that this is no longer the case when there is a large number of flux changes per revolution, in other words in magnetos which are built for a large number of sparks and run at a high rotational speed, for example in magnetos for modern aircraft engines. The steepness of a flux half-wave decreases with increasing flux change frequency. Disturbances are thereby produced which may increase until the ignition is completely suspended.

The present invention aims at obviating this risk by the fact that the breaker remains open, after it has opened, at least for the duration of a half flux wave, for the purpose of preventing detrimental short-circuit current during the fiux changes not utilised for ignition.

In the annexed drawing Fig. 1 represents a diagram of the electrical connections.

Fig. 2 shows a number of curves illustrating the magnetic flux,

Fig. 3 part of the development of the circumference of a breaker cam wheel and Fig. 4 a view of a multidivisional breaker cam wheel with the breaker lever.

Figure 1 of the accompanying drawing shows an arrangement, by way of example, of the magneto circuits of a magneto (which is not further illustrated) having a multi-pole magnet and Winding part.

In Figure 1,E, Pr, 0 and U, E designate the primary circuit, S the secondary circuit with the spark gap (sparking plug) K; connected in the primary circuit is the breaker lever U, operated by a cam wheel (not illustrated) having many cams, and the condenser C connected in parallel therewith. A bridging resistance W, electrically connected with the primary circuit and with the condenser C, is connected to a contact I which is disposed in the range of the breaker lever and against which the latter automatically bears when opened.

When the breaker is closed, a short-circuit current flows in the primary winding. If a flux halfwave is to be utilised for ignition, the breaker is opened approximately at the moment when the current reaches its maximum. At that moment the flux, which in consequence of the shortcircuit current reaction is considerably smaller than when the breaker is open, darts to the value that it would have attained at that moment if the breaker were constantly open.

But if the breaker is not opened, the magnetic field is weakened during the entire flux halfwave.

In Figure 2 of the accompanying drawing are shown some flux or current curves in the magnetic field during a flux change period, which illustrate the foregoing statements.

The curve a shows by way of example the fiux course in the magnetic field when the breaker is opened at the current maximum.

Curve b shows the current course in the event of breaking every current half-wave.

Curve 0 shows the course of the magnetic flux in the magnetic field when the breaker is closed.

Curve d illustrates the current course when, as hitherto, the breaker remains closed during the unutilised fiux half-wave.

Curve e shows the current course in the primary circuit in a magneto controlled in accordance with the present invention. The breaker lever U in Fig. 3 is so controlled that it remains open, after opening at e, for a complete semiperiod, i. e. until e" in the first part of the second semi-period. During this time no detrimental short-circuit current fiows in the primary winding, contrary to the hitherto customary control of the breaker, in which the latter is closed again directly after opening (curve d). As a consequence of this the current maximum in the next half-wave is substantially increased in consequence of earlier passage through the zero line and the greater steepness of the flux course by comparison with that in the curve d. From this it is clear that at the moment of the interruption of current, even in the case of a very high frequency of flux changes or very high number of sparks, the voltage required for dependable ignition is reached in the secondary winding.

It is naturally possible to keep the breaker open not merely during a half flux wave, but during two or more entire periods, if this is required by circumstances.

Thus in Figure 3 F shows a range of curves where in a magneto with 12 sparks every revolution of the breaker keeps open the primary circuit during three subsequent periods for regulating a four cylinder motor.

The no-load voltage produced when the breaker is open can be reduced in simple manner by bridging over the breaker, during the opening time of the latter, by the resistance W which allows a part of the short-circuit current to fiow.

It is simple to adjust this resistance in such a manner that the voltage on the secondary side is reduced to the desired extent and that nevertheless the influencing of the fiux change utilised for the ignition is so small that the dependability of the ignition is not impaired.

The bridging resistance is preferably connected by the breaker lever itself.

Instead of a resistance connected to the primary circuit, for bridging over the opened breaker, the high tension distributor could for instance be provided with contacts on the circumference or with cable connections, operative for the ignition, the number of which would correspond with the number of breaker points of the cam Wheel operating the breaker, so that during the flux changes not utilised for ignition no connection would be made by the distributor to the sparking plugs. The no-load voltage of the transformer can then be returned directly to frame by way of a contact.

In Figure 4 a cam wheel U is shown having 14 cams n and the breaker lever U is shown in an intermediate position where the breaker lever is neither in contact with j the contact of the branch circuit W nor with contact f of the primary circuit. The lines n bridging the gaps between every two cams n represent a breaker wheel having 7 cams. These two cams correspond to engines having 14 or 7 cylinders.

What I claim is:

1. In an ignition system for a multipole magneto, the combination of a primary ignition circuit including a make and break switch and a condenser in shunt with said switch, a secondary circuit including a. spark gap, a cam disc shaped and arranged to open said make and break switch every time a spark is to be produced and to retain said switch in its open position at least for the duration of a half flux wave in the magneto, a normally open shunt circuit across said make and break switch and said condenser, said shunt circuit including a resistance, and means to close the shunt circuit after the make and break switch has been opened and to keep said shunt circuit closed substantially until the make and break switch is closed again.

2. In an ignition system for a multipole magneto, the combination of a primary circuit connected to the magneto and including a fixed contact and in series with said fixed contact a condenser connected to ground, a movable contact connected to ground and normally cooperating with said fixed contact to short-circuit said primary circuit across said condenser, a cam disc shaped to displace said movable contact and to break the direct connection of said primary circuit to the ground every time a spark is to be produced for the duration of at least a half fiux wave in the magneto, and a normally open shunt circuit connected in said primary circuit and including a resistance and a second fixed contact arranged for cooperation with said movable contact when the latter has been displaced by said cam, whereby said shunt circuit is closed after each breaking of the direct connection between said primary circuit and the ground.

WALTER OCHSENBEIN. 

